Field of the Invention
The invention relates to an optical system and a display apparatus, and particularly relates to an illumination system and a projection apparatus.
Description of Related Art
In recent years, projection apparatuses using solid state light sources such as light emitting diodes (LEDs) and laser diodes are more and more popular on the market. Since laser diodes have a high light emitting efficiency, to break through the limitation of LED light sources, pure color light sources generated by exciting fluorescence and designed form projectors are developed. Besides, in addition to emitting light by exciting fluorescence using laser light sources, laser light may also be directly used as the illuminating light source of a projector in laser projection apparatuses. As laser light has the advantage of being able to adjust the number of light sources based on the brightness requirement, the brightness requirements of various projectors can thus be met. Therefore, the projector structure adopting a light source system using the laser light source has a high potential of replacing the conventional ultra high pressure mercury lamp and becoming the light source of the next-generation projectors.
The conventional laser projectors use a laser light source and make the laser light focus on a fluorescence layer to output fluorescent light with enough intensity. However, the light spot formed by using semiconductor laser is has a shape similar to an ellipse, and the light intensity distribution thereof is similar to a Gaussian distribution. On the other hand, the light spot of the light beam emitted by exciting the fluorescence using laser light is similar to a circular shape and the light intensity distribution thereof is similar to a Lambertian distribution. When the laser beam and the light beam generated by exciting the fluorescence are combined, the illumination is not uniform due to differences in the shapes of light spots and the light intensity distributions. Therefore, the color in an image frame projected by the laser projection apparatus is not uniform, either.
To solve this issue, it is common to dispose a Lambertian diffuser on the path of the laser beam and make the light beam converge on the Lambertian diffuser based on the requirement of a general optical structure. The Lambertian diffuser diffuses the laser beam, such that the shape and size of the light spot and the light intensity distribution of the laser beam become similar to those of the light beam emitted by exciting the fluorescence, so as to make the color of the image frame of the projection apparatus uniform. However, the Lambertian diffuser is very costly. Besides, since the light intensity per unit area at the center of the light spot formed by the laser beam having a light intensity distribution similar to the Gaussian distribution is higher, the energy density is high when the light beam directly converges on the Lambertian diffuser. Thus, there is a risk that the Lambertian diffuser may be burnt.
The information disclosed in the “Description of Related Art” section is only for enhancement of understanding of the background of the described technology, and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Further, the information disclosed in the “Description of Related Art” section does not mean that one or more problems to be resolved by one or more embodiments of the invention were acknowledged by a person of ordinary skill in the art.